FIG. 45 to FIG. 47 are schematic views showing a configuration of a conventional droplet discharge device 9. FIG. 45 is a perspective view of the droplet discharge device 9, FIG. 46 is a lateral cross-sectional view of the droplet discharge device 9, which is taken along XLVI-XLVI of FIG. 45, and FIG. 47 is a longitudinal cross-sectional view of the droplet discharge device 9, which is taken along XLVII-XLVII of FIG. 45.
As shown in FIG. 45 to FIG. 47, the droplet discharge device 9 has a structure in which a plurality of vibrators 920 are arranged in a regular manner on an upper surface 9021 of a substrate 902.
As shown in FIG. 46 and FIG. 47, the substrate 902 has a structure in which cavities 908, discharge holes 910 and supply holes 912 which serve as a liquid flow path are formed inside a plate. The cavities 908 are separated from the upper surface 9021 of the substrate 902 by a vibration plate 904. With such a structure, the vibration plate 904 is subjected to bending vibration by the vibrators 920 fixedly installed on an upper surface 9041 of the vibration plate 904, and then liquids filled in the cavities 908 are pressed, whereby droplets are discharged from the discharge holes 910.
As shown in FIG. 46 and FIG. 47, in the conventional droplet discharge device 9, the cavity has uniform lateral width W91, longitudinal width W92 and depth D91. This is because a ceramic green sheet subjected to punching process with a die, a ceramic green sheet subjected to drilling process by a laser beam, or the like was subjected to thermocompression bonding and then subjected to firing to manufacture the substrate 902, and accordingly, inner side surfaces 9081 to 9084 of the cavity 908 have to be perpendicular to the upper surface 9021 of the substrate 902, and an inner lower surface 9086 of the cavity 908 have to be parallel to the upper surface 9021 of the substrate 902.
Patent Document 1 is a prior art reference which describes the invention known to the public through publication concerning a conventional droplet discharge device. Also in a liquid drop emitter described in Patent Document 1, a cavity has uniform width and depth.
Patent Document 2 is a prior art reference which describes the invention known to the public through publication related to the present invention. Patent Document 2 describes a liquid discharge device (inkjet head 1) in which a width of a cavity (ink chamber 5) becomes narrower toward a discharge hole (nozzle 8) side, and a depth of the cavity becomes deeper toward the discharge hole side. In the droplet discharge device of Patent Document 2, an upper end of a vibrator (piezoelectric element 13), in which piezoelectric/electrostrictive films and electrode films are assumed to extend to be perpendicular to a main surface of a substrate and to be alternately laminated, is fixed to a vibration plate (vibration film 3), whereby expansion and contraction of the vibrator in a direction perpendicular to the main surface of the substrate are transmitted to the vibration plate.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-075305    Patent Document 2: Japanese Patent Application Laid-Open No. 2002-036538